Problem: Simplify the following expression: $a = \dfrac{n^2 - 2n - 24}{n + 4} $
Solution: First factor the polynomial in the numerator. $ n^2 - 2n - 24 = (n + 4)(n - 6) $ So we can rewrite the expression as: $a = \dfrac{(n + 4)(n - 6)}{n + 4} $ We can divide the numerator and denominator by $(n + 4)$ on condition that $n \neq -4$ Therefore $a = n - 6; n \neq -4$